Semiconductor wafers are typically processed in specialized processing systems. These systems include one or more chambers, each performing wafer processing operations such as etching, chemical vapor deposition or physical vapor deposition, which often require heating or cooling of the wafer, and a plasma to assist the process. Each chamber includes inlets and outlets for admission and evacuation of processing gases, as well as an aperture controlled by a slit valve to admit wafers. Such processing chambers may in turn communicate with a wafer transfer chamber, and in turn the transfer chamber will have a valve-controlled aperture by which wafers can be admitted from outside the system. Importantly, the fabrication of semiconductors and the handling of silicon wafers requires exceptional cleanliness. Therefore, the environment within such processing chambers and storage areas must be maintained virtually free of dust and contaminants. In order to minimize risk of contamination, the transfer of a wafer to and from a chamber and to and from the outside of the system is generally done mechanically by means of a robot arm at the end of which is a wafer retaining means.
Semiconductor wafers are typically stored in a wafer storage cassette that retains a plurality of wafers vertically in a spaced apart relationship. One standard type of wafer retaining means used in the art includes a flat blade-like arm through which a vacuum conduit is formed, terminating in an outlet. This is so that the arm can pick up a wafer by touching the surface containing the outlet, typically the upper surface of the arm, to the bottom surface of the wafer and applying a vacuum, so as to cause the wafer to stick to the arm. The vacuum-held wafer is securely retained to the arm as the robot arm swings around to deliver the wafer to another location. The advantage of the flat vacuum arm pickup is that the arm, being flat and thin, can be relatively easily maneuvered between the closely spaced wafers in a wafer storage cassette to retrieve and transfer a wafer therefrom.
Prior art wafer transfer arms are typically constructed as a solid, unitary member comprised of a durable heat resistant material such as a metal, plastic, or ceramic, for example, or as a multi layer laminate of metal and plastic bonded together with silicone rubber or some other appropriate adhesive.
Prior art wafer transfer arms are typically fashioned by cutting a longitudinal channel along a surface of the arm and adhesively attaching a thin plastic film covering comprising, for example, a polyamide material, to the surface for sealing the channel to form a gas-tight conduit between a vacuum outlet and inlet of opposing ends of the arm, respectively. However, such wafer transfer arms manifest limited useful lives and often suffer from critical disadvantages as will be explained hereinafter.
One drawback associated with prior art wafer transfer arms, is premature wear and deterioration. During normal operation, the arm is typically exposed to high temperature, corrosive conditions created by the presence of wafer processing gases and liquids, and stress associated with the cycling of subatmospheric pressures within the arm. The unfavorable conditions greatly impact the thin plastic film covering, herein referred to as the "coverplate", frequently resulting in rapid deterioration and detachment from the surface of the arm. As the coverplate peels back, the loose end poses a danger of scratching the delicate surface of a neighboring wafer during retrieval, ruining the whole wafer. The loosened or damaged coverplate may also lead to a total or partial loss of vacuum in the arm, thereby compromising the wafer retaining capability and resulting in the dropping and loss of retrieved wafers.
Another serious drawback associated with the prior art wafer transfer arms is the tendency of the arm to crack or break unexpectedly during normal use. The wafer transfer arm's thin profile and the longitudinal channel severely diminishes the tensile strength of the arm resulting in abrupt structural fatigue and failure. Moreover, the thin film coverplate affixed to the surface of the arm contributes little or none to the overall structural integrity of the arm. Such failures are unacceptable and costly in semiconductor wafer processing systems.
For the foregoing reasons, there is a need for an improved device, that is durable, reliable, and long-lasting while remaining simple and cost effective to fabricate. Also very desirable would be a wafer transfer arm that consistently assures proper holding and centering of the wafer under various conditions and environments encountered during wafer transferral. It would also be very advantageous to provide a wafer transfer arm that can withstand corrosive substances, elevated temperatures, and repeated cycling of subatmospheric pressures for retaining, for example, silicon wafers. The foregoing capabilities would be still more desirable if provided with a thin profile wafer transfer arm with the capability of smoothly accessing individual wafers between the tight spaces of standard wafer storage cassettes, and which the arm incorporates a vacuum conduit means for retrieving and retaining the wafers.